It is sometimes explained as an expression of courtesy--"I obey thee as a superior"; which does not occur elsewhere, because it is not Hebrew but Egyptian. But this suavity is quite alien to the spirit of the narrative, in which Moses, however courteous, represents an offended God. It is more natural to take it as an open declaration that he was being imposed upon, yet would grant to the king whatever advantage the fraud implied. And to make the coming relief more clearly the action of the Lord, to shut out every possibility that magician or priest should claim the honour, he bade the king name an hour at which the plague should cease.
If the frogs passed away at once, the relief might chance to be a natural one; and Pharaoh doubtless conceived that elaborate and long protracted intercessions were necessary for his deliverance. Accordingly he fixed a future period, yet as near as he perhaps thought possible; and Moses, without any express authority, promised him that it should be so. Therefore he "cried unto the Lord," and the frogs did not retreat into the river, but suddenly died where they were, and filled the unhappy land with a new horror in their decay.
But "when Pharaoh saw that there was respite, he made his heart heavy and hearkened not unto them." It is a graphic sentence: it implies rather than affirms their indignant remonstrances, and the sullen, dull, spiritless obstinacy with which he held his base and unkingly purpose.